Incomplete nitrification: ammonia riding through on the permit
Nitrification is the oxygen-hungry step where bacteria convert ammonia to nitrate. Those bacteria are slow growers and among the first to feel a shortage of dissolved oxygen, so when the level sags the step stalls and ammonia rides through to the effluent. Holding oxygen steady keeps the conversion complete against the permit.
What’s actually happening in your water
Nitrification is the step that turns ammonia into nitrate. A specialized group of bacteria in the activated sludge, the suspended culture that does the treatment, carries it out, and the conversion consumes dissolved oxygen (DO, the oxygen carried in the water) to run. Ammonia (the nitrogen form that arrives with the waste and that many permits cap) only leaves the plant as nitrate if these bacteria finish their work.
Those nitrifiers are slow growers, and they are among the first to feel a shortage of oxygen. When the dissolved oxygen in the aerated zone sags below what they need, the conversion stalls, and the ammonia that would have become nitrate rides through to the effluent instead. So an ammonia reading over the limit is usually a picture of nitrification that ran short of oxygen, not a new problem of its own.
That shortage is the same one behind a basin whose aeration cannot keep up under load. The nitrifiers just show it first, because they are the least forgiving part of the culture.
Why the usual fixes don’t hold
Chasing the ammonia number before a sampling date, nudging chemistry or holding solids longer, treats the report and not the culture. If the aerated zone is still short of oxygen, the nitrifiers stay slow and the next reading comes back where it was.
Pushing the blowers harder does add oxygen, and it adds power cost fast, because most of the air from a coarse-bubble grid leaves at the surface before it dissolves. The nitrifiers only use the oxygen that actually reaches the water, so a great deal of the energy does nothing for the step you are trying to finish.
How restoration works here
Continuous nanobubble oxygenation keeps the oxygen the nitrifiers need available in the water. Nanobubbles stay suspended and give their oxygen up in the water rather than the air, so the aerated zone holds a steadier level for the slow-growing culture to work in. With oxygen held, the population recovers over weeks and the conversion of ammonia to nitrate runs to completion again.
What we do not do is promise a permit number or claim the whole total-nitrogen result. Removing nitrate is denitrification, a separate step that happens without oxygen, so we measure the ammonia and the nitrogen forms against a baseline and report which the oxygen moved. Your permit and process control govern; we integrate with them. What we measure and how is published, so the readings you show an inspector are ones we can both stand behind.
What to expect, and when
Days 1-14
We baseline the dissolved oxygen in the aerated zone and the ammonia the plant already samples, so any change is read against a number. Because dissolved oxygen is a live reading, whether the aerated zone actually holds enough of it shows early.
Weeks 3-12
Nitrifiers are slow to build, so a stalled population recovers over weeks, not days, as the oxygen it needs stays available. The ammonia readings the permit turns on are logged against the baseline through that recovery rather than predicted.
Season and beyond
Cold water slows nitrification every winter, so a full season shows whether the aerated zone holds enough oxygen to keep the step complete through the hard months. The record is kept either way.
The record
We don't have a published case file for this problem yet. Every Alchemal installation is instrumented from day one, so the first case files are being measured now, and until one is ready, our methodology shows exactly what we record and how we report it.
When this isn't the right fix
- Total nitrogen is more than nitrification. Converting ammonia to nitrate is the aerobic half; removing that nitrate is denitrification, a separate step that happens without oxygen. Oxygenation supports the nitrification side and is measured, not a promise on the whole nitrogen number.
- If the nitrifiers are being lost to a toxic slug, a washout, or a sludge age held too short for them to grow, oxygen keeps the survivors working but will not rebuild a population the process is shedding. The assessment reads which it is.
- A permit and its limits govern, and we integrate with your process control rather than replace it. The readings we take are chosen to be the kind an operator and an inspector recognize.
Questions people ask
What is nitrification and why does it need oxygen?
Nitrification is the two-step conversion of ammonia to nitrate by specialized bacteria. That conversion consumes oxygen, so the bacteria only work where dissolved oxygen is available. They are slow-growing and sensitive, which is why a shortage of oxygen shows up as incomplete nitrification before it shows anywhere else.
Why is ammonia high in our effluent?
Effluent ammonia climbs when nitrification does not finish. The usual reason is that the nitrifiers ran short of the dissolved oxygen the step needs, so the ammonia passes through unconverted. Cold water, a heavier load, or a sagging DO setpoint all push the step toward incomplete, and the ammonia reading follows.
Does oxygenation lower total nitrogen too?
Only the nitrification half. Holding oxygen helps convert ammonia to nitrate reliably, but removing that nitrate is denitrification, which happens in an anoxic zone without oxygen. We measure the ammonia and the nitrogen forms against a baseline and say which the oxygen moved rather than claim the whole total-nitrogen number.
Will this help nitrification through the winter?
It can support it, because cold water both slows the nitrifiers and holds more oxygen, so the limit through winter is often whether the aerated zone keeps enough available. Holding oxygen steady removes that as the constraint. Whether it is enough depends on the temperature and the load, which is why we log a full season.
Can you guarantee we meet our ammonia limit?
No. Whether the effluent meets an ammonia limit depends on your load, your basin, your sludge age, and the limit itself, none of which a system alone sets. What we offer is a measured DO baseline, oxygen held where the nitrifiers need it, and the ammonia logged against the baseline so the direction is something you can check.
Tell us what your water is doing.
A specialist reads your description and replies in writing: what it usually means and what we would measure first.